Method of manufacturing magnetic recording medium

ABSTRACT

A method and apparatus for manufacturing a magnetic recording medium using vacuum-deposition from an evaporated metal source having a very high efficiency and uniform deposition. The support onto which the magnetic film is to be evaporated is guided and conveyed along a curved path above a molten metal evaporating source at a substantially constant speed. The curved path is shaped such that evaporated metal flow lines connecting a central point on the evaporation surface of the molten metal in the evaporating source to corresponding intersection points on the support form the same angle of incidence with respect to the longitudinal direction of the support for all positions along the support where the film is to be deposited. Endless belt structures including guide rollers and magnets are used to form rising and falling paths for conveying the support along the desired curved path.

BACKGROUND OF THE INVENTION

The present invention relates to a so-called "oblique incidence vacuumdeposition" method in which a magnetic material is applied by vacuumdeposition obliquely to a flexible belt-shaped support beingcontinuously conveyed to thereby manufacture a magnetic recordingmaterial.

Recently, as the demand for high-density magnetic recording hasincreased, instead of the conventional magnetic recording mediummanufacturing method in which a binder type magnetic solution is coatedon a flexible support and dried, a variety of non-coating systemmagnetic recording medium manufacturing methods in which, without usinga binder, a ferromagnetic metal film layer is formed on a support byvacuum deposition, sputtering, ion plating, or the like have become ofincreased interest.

Among the non-coating magnetic recording medium manufacturing methods,an oblique incidence vacuum deposition method in which beams ofevaporated magnetic metal are applied obliquely to the surface of asupport so as to be desposited thereon has been found to be quitepractical because the process is simple and the apparatus needed forimplementing the method is relatively compact. Moreover, the methodprovides a magnetic film layer having excellent magneticcharacteristics.

A specific feature of conventional oblique incidence vacuum depositionis that, while the support is being conveyed straightly or along theouter wall of a cylindrical drum, i.e. along a curved line, above theevaporating source, a ferromagnetic metal film is vacuum-deposited inone step on the support surface to a predetermined thickness by theevaporated metal beam from the evaporating source with the application(incident) angle of the beam being strictly limited. However, as theevaporated beam is oblique with respect to the support surface, thethickness of the vacuum-deposited metal film is equal to the cosine ofthe angle of incidence multiplied by the thickness of a vacuum-depositedmetal film which would be formed with a zero incidence angle (where theevaporated metal beam forms a right angles with the support surface).Therefore, it is unavoidable that as the incident angle is increased,the efficiency of vacuum deposition is decreased. In addition, if thegeometrical arrangement of the support and the evaporating source issuch that the incident angle is increased, then the distance between thesupport and the evaporating source is correspondingly increased, andaccordingly the efficiency of vacuum deposition is further decreased.Since the magnetic characteristics of the vacuum-deposited magnetic filmdepend on the incident angle (see, for example, Japanese publishedpatent application No. 352,558--1964), it is essential that the incidentangle be as small as possible and that it be maintained unchanged duringcoating operations.

A low efficiency of vacuum deposition makes it difficult to decrease themanufacturing cost when a relatively expensive nonferrous metal such ascobalt or cobalt alloy is used. Accordingly, this has been a seriousproblem requiring solution before the method can be put to practicaluse.

In order to solve the problem, for instance, as proposed in JapanesePatent Laid-Open Application No. 9607/1979, a method can be used inwhich the evaporating source is shifted from the position immediatelybelow the drum so that only a high-density portion of the evaporatedmetal beam is applied to the surface of the support on the outer wall ofthe drum. Using this method, the efficiency of vacuum deposition is 20%.

However, with this method, it is difficult to increase the range ofsuitable evaporated metal beam incident angles with respect to thesupport on the outer wall of the drum. Accordingly, further improvementof the efficiency of vacuum deposition for a given evaporating source islimited. Further, the method must be significantly improved if theefficiency of vacuum deposition is to be made satisfactory. The methodis also disadvantageous in that the resultant magnetic recording mediumdoes not have uniform magnetic characteristics if an incident anglelarger than a particular angle is used.

Accordingly, an object of the invention is to provide a magneticrecording medium manufacturing method in which all of theabove-described problems relating to the efficiency of vacuum depositionof the conventional oblique incidence vacuum deposition method have beeneliminated.

It is a further object of the invention to provide a method formanufacturing a magnetic recording medium having a high anti-magneticforce and high rectangular ratio.

SUMMARY OF THE INVENTION

The foregoing object and other objects of the invention have beenachieved by the provision of a magnetic recording medium manufacturingmethod and apparatus in which, according to the invention, a flexiblebelt-shaped support is guided and run along a curved path in such amanner that, while the flexible belt-shaped support is being conveyedabove a molten metal evaporating source substantially at a constantspeed, evaporated metal flow lines connecting a central point of theevaporation surface of the molten metal evaporating source tocorresponding intersecting points on the support form the same incidentangle with respect to the longitudinal direction of the support at alltimes, wherein a magnetic film is efficiently and uniformlyvacuum-deposited on the surface of the support.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory diagram for a description of evaporating metalin an apparatus for practicing a method according to the invention;

FIG. 2 is a schematic diagram showing essential parts of an apparatusfor practicing the method of the invention;

FIG. 3 is an enlarged view showing the relation between an evaporatedmetal flow line and a curved web in FIG. 2; and

FIG. 4 is a perspective view showing an essential portion of anotherexample of web transfer means.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of a method of manufacturing a magnetic recordingmedium will be described with reference to the accompanying drawings.

FIGS. 1 and 2 show an apparatus for practicing the method of theinvention. In FIG. 1, reference numeral 1 designates a supply ofevaporated metal which is provided by scanning an electron beam onto ametal in a water-cooling copper hearth 2 which extends in the widthwisedirection of a flexible belt-shaped support, web W. The metal vapor 1diffuses and evaporates along evaporated metal flow lines as indicatedby arrows 3 in FIG. 1. A specific feature of the method of the inventionis that, while the web W is being guided in such a manner as to form acurved loop above the hearth 2, a metal film layer is formed on thelower surface, facing the hearth 2, of the web W.

A structure for guiding the web W along the curved loop is shown in FIG.2. Guide rollers 4 through 9 are provided at points where the directionof run of the web W is to be changed with the guide rollers 4 through 9directly supporting the web W. Among the guide rollers, the rollers 4and 5 and the rollers 8 and 9 form a rising path A of the web W and afalling path B of the web W, respectively, which are symmetrical withrespect to the hearth 2. Endless-belt shaped curve forming mechanisms 10and 10' are provided between the rollers 4 and 5 and between the rollers8 and 9, respectively.

The curve forming mechanism 10 and 10' have endless belts 11 and 11',respectively, each of which is formed as follows: Metal such as copperor aluminum is vacuum-deposited on the outer side of a plastic belt, onthe inner side of which an iron film, a fine iron wire or iron powder isprovided. The endless belts 11 and 11' thus formed are laid over aplurality of guide rollers 12 and 12', respectively. A plurality ofmagnets 13 and 13' are suitably disposed adjacent to the inner sides ofportions of the endless belts 11 and 11' forming the abovedescribedrising path A and falling path B of the web W, respectively. The magnets13 and 13' continuously attract the endless belts 11 and 11' so that thebelts curve along the rising path A and the falling path B,respectively. Each of the endless belts 11 and 11' may be replaced by acaterpillar-type belt which is provided by connecting a number ofelongated iron plates. In case of the employment of the caterpillar-typebelt, as shown in FIG. 4, it is also possible to guide the travel of thebelts 16 along the rising path A and the falling path B in such a mannerthat each of the belts 16 at its surface confronting the evaporatedmetal flow lines is supported by means of a plurality of guide rollers18 each rotatably supported to a pair of supporting plates 17. The bothends of each of the belts 16 are guided by these rollers 18.

The web W running along the curved rising path A and the curved fallingpath B is electrostatically charged by a glow discharge process or thelike before it confronts the hearth 2. Therefore, the web W iselectrostatically attracted to the outer sides of the endless belts 11and 11' in the rising path A and the falling path B so that it is guidedin the form of a curve.

The shape of the curve forming mechanisms 10 and 10' is determined asfollows. As shown in FIG. 3, the evaporated metal flow line 3'connecting the central point O of the evaporation surface of the metalvapor 1 to a given point X on the web W along the rising path A (or thefalling path B) forms an angle ∠YXO with a line XY tangent to the pointX. The curve forming mechanism is designed so that it conveys the web Wwith a curvature so as to maintain the angle ∠YXO constant in thelongitudinal direction of the web W.

In the regions where the lower portions of the rising path A and thefalling path B are located and the two paths A and B come closest toeach other, it is desirable that shielding masks 15 and 15' be providedbetween the hearth 2 and the guide roller 4 and between the hearth 2 andthe guide roller 9, respectively, and that a shielding mask 14 bedisposed between the guide rollers 5 and 8 in order to eliminatedifficulties in deposition quality which can be caused if the density ofevaporated metal flow lines of the evaporated metal 1 is excessively toosmall or in areas where it is difficult to curve the web W so that theabove-described incident angle is maintained.

In the above-described method of the invention, while the web W ispassing above the hearth 2 substantially at a constant speed, the web Wis guided along the curves by the curve forming mechanisms 10 and 10' insuch a manner that the evaporated metal flow lines connecting thecentral point O of the evaporation surface of the evaporated metal 1 inthe hearth 2 to a given point on the web W form the same incident angleθ with respect to the longitudinal direction of the web W. With thisconstruction, the efficiency of vacuum-deposition of the evaporatedmetal 1 is greatly improved and the resultant magnetic characteristic isuniform.

In order to confirm the efficiency of vacuum-deposition according to themethod of the invention, first utilizing only the rising path A in FIG.2, cobalt was vacuum-deposited on a conveyed polyester film of thickness12 μm, and second utilizing both the rising path A and the falling pathB, cobalt was vacuum-evaporated on the same film. In the former case,the efficiency of vacuum-deposition was 25% while in the latter case itwas 52%.

The magnetic characteristics of a vacuum-deposited cobalt film formedaccording to a method proposed by Japanese Laid-Open Patent ApplicationNo. 9607/1979 among the abovedescribed conventional methods, especiallythe anti-magnetic-force and rectangular ratio thereof, were comparedwith those of a vacuum-deposited cobalt film formed according to theabovedescribed method of the invention. The anti-magnetic-force and therectangular ratio of the film according to the conventional method were850 Oe and 0.91, respectively, while those of the film according to themethod of the invention were 900 Oe and 0.95. Thus, it has beenconfirmed that the method of the invention provides excellent magneticcharacteristics.

In manufacturing a magnetic recording medium according to the vacuumdeposition method of the invention, metal such as Fe, Co or Ni may beemployed as a ferromagnetic metal to form a magnetic film, orferromagnetic alloys such as Fe-Co, Fe-Ni, Co-Ni, Fe-Co-Ni, Fe-Rh,Fe-Cu, Co-Cu, Co-Au, Co-Y, Co-La, Co-Pr, Co-Gd, Co-Sm, Co-Pt, Ni-Cu,Mn-Bi, Mn-Sb, Mn-Al, Fe-Cr, Co-Cr, Ni-Cr, Fe-Co-Cr, or Fe-Co-Ni-Cr maybe employed. The magnetic film should be thick enough to provide asufficient output as a magnetic recording medium and thin enough forhigh density recording operations. Taking these considerations intoaccount, in general, the thickness of the magnetic film should be in arange of from about 0.02 μm to 5.0 μm, preferably from 0.5 μm to 2.0 μm.

A plastic base support, for instance, of polyethylene terephthalate,polyimide, polyamide, polyvinyl chloride, cellulose triacetate,policarbonate or polyethylene naphthalate may be employed as the supportW.

A resistance heating method, a laser beam heating method, a highfrquency heating method or an electron beam heating method can beemployed to heat the evaporation source in accordance with theinvention. A method of feeding a linear material to the heating sourcemay be employed to feed the evaporation material.

An apparatus for practicing the method of the invention has beendescribed with reference to the case where both the rising path A andthe falling path B are used simultaneously. However, if necessary, onlyone of the two paths A and B can be used.

What is claimed is:
 1. A method of manufacturing a magnetic recordingmedium comprising the steps of: evaporating molten metal from a metalevaporating source; and transporting a flexible belt-shaped supportabove said evaporating source at a substantially constant speed along acurved path forward such that evaporated metal flow lines connecting acentral point on an evaporation surface of said molten metal to saidsupport from a substantially constant angle of incidence with respect toa longitudinal direction of said support throughout an area where saidevaporated metal flow lines contact said support.
 2. The method of claim1 wherein said step of transporting said support comprises providingfirst and second guide rollers upon either side of said source;providing at least third and fourth rollers in upper positions alongsaid curved path; and providing first and second endless-belt shapedcurve forming mechanisms on opposite sides of said curved path.
 3. Themethod of claim 2 wherein said endless-belt shaped curve formingmechanisms each comprise an endless belt; a plurality of guide rollersfor transporting said endless belt, said guide rollers being positionedso as to guide said endless belt along a predetermined portion of saidcurved path; and a plurality of magnets disposed within said endlessbelt for attracting said endless belt.
 4. The method of claim 3 whereineach of said endless belts comprises a plastic belt having a layer ofmetal vacuum deposited on an outer surface thereof and an iron film onan inner surface thereof.
 5. The method of claim 4 wherein saidvacuum-deposited metal layer comprises a metal selected from the groupconsisting of copper and aluminum.
 6. The method of claim 4 wherein saidiron layer comprises a material selected from the group consisting ofiron film, fine iron wire and iron powder.
 7. The method of claim 3further comprising the step of electrostatically charging said flexiblebelt-shaped support wherein said support is electrostatically attractedto outer surfaces of said endless belts.
 8. The method of claim 3wherein shielding masks are provided in areas closely adjacent saidfirst and second rollers between said first and second rollers and saidsource and shielding means is further provided at an upper portion ofsaid curved path below said third and fourth rollers and between upperportions of said endless belts for shielding said flexible belt-shapedsupport.
 9. The method of claim 1 wherein a film layer of said metal isformed on said support to a thickness in a range of 0.02 μm to 5.0 μm.10. The method of claim 1 wherein a film layer of said metal is formedon said support to a thickness in a range of 0.05 μm to 2.0 μm.
 11. Themethod of claim 1 wherein said belt-shaped support is formed from amaterial selected from the group consisting of polyethyleneterephthalate, polyimide, polyamide, polyvinyl chloride, cellulosetriacetate, polycarbonate and polyethylene naphthalate.
 12. A method ofmanufacturing a magnetic recording medium comprising the steps of:evaporating molten metal from a metal evaporating source; andtransporting a flexible belt-shaped support relative to said evaporatingsource along a curved path formed such that evaporated metal flow linesconnecting a central point on an evaporation surface of said moltenmetal to said support form a substantially constant angle of incidencewith respect to a longitudinal direction of said support throughout anarea where said evaporated metal flow lines contact said support.
 13. Amethod of claims 1 or 12, wherein one side of the belt-shaped support iscoated by vacuum evaporation of molten metal.